1. Field of the Invention
The present invention relates to an optical branching device connected to a light output end face of an optical waveguide device or another optical branching device for branching input light.
2. Description of the Related Art
A general optical branching device is comprised of an input optical waveguide, a taper-shaped transition region for adiabatically changing a light distribution, and respective branching optical waveguides.
Although the optical branching device is designed so that optical powers propagated to the respective branching optical waveguides have desired values, a measured value of a branching characteristic of a fabricated optical branching device often becomes a value different from a calculated value of the branching characteristic. In an actual optical branching device, a light output end face of an optical fiber is connected to a light input end face of an input optical waveguide, however, while a section of the optical fiber orthogonal to its axis is circular, a section of the optical waveguide orthogonal to its axis is rectangular, and therefore, both have different eigen modes. Accordingly, in the connection structure of the input optical waveguide and the optical fiber, it is impossible to avoid the occurrence of a leaky mode caused by mismatching of mode solution distributions of those.
Since the magnitude of the occurring leaky mode also includes a previously expected coupling loss and a coupling loss which can occur by fiber connection or the like, it is very difficult to prepare an optimum design in view of the actual leaky mode. Accordingly, in order to suppress branching ratio variation of the optical branching device caused by a subtle difference of a connection state between the optical fiber and the input optical waveguide, very accurate optical axis alignment is required at the time of connection of the optical fiber and the input optical waveguide. Thus, there arises a problem that the connection operation of the optical fiber and the input optical waveguide becomes troublesome and yield becomes low.